The invention relates to an extrusion molded, preferably ceramic, facade panel for the curtained, back-ventilated mounting on a sub-structure, wherein the facade panel (11) consists of a front and rear panel framework (12,13) which are connected to one another by webs (14) and are provided with elongate apertures (15) which are arranged parallel to the web (14) between the same and which is provided with a top rabbet (16) at the upper end of the facade panel (11).
Extrusion moulded ceramic facade panels in upright format are known from DE 43 25 873 which are formed by a front and a rear panel formwork, which are connected to one another by vertically extending webs and are provided with elongate apertures which are arranged between the webs. At the top-side edge of these facade panels, the protruding rear panel formwork forms a top rabbet which is higher than the height of the horizontal joint visible from the front side which is formed by two facade panels arranged above one another. At the bottom-side edge of the facade panels, the protruding front panel formwork forms a bottom rabbet which is higher than the height of the horizontal joint between facade panels arranged above one another visible from the rear side of the facade. The facade has a visually closed appearance from the outside (and also from the inside) due to the top and bottom rabbets gripping behind one another. Furthermore, an optimum water guiding of the facade water running off at the front side of the facade results, as does the possibility to attach the panel holders in a largely covered manner. The disadvantage of this construction can be found in the fact that the top and bottom rabbets extend transversely to the direction of extrusion moulding so that these cannot be simultaneously extruded in the extrusion moulding process. The only possibility that therefore remains is to apply the top and bottom rabbets to the facade panels in a plastic, dried or burnt state. In the manufacture of the top or bottom rabbets in the plastic state, very coarse, unacceptable tolerances result in the burnt facade panel due to the unavoidable ceramic shrinkage differences. In the manufacture in the dried state, e.g. by cutting, intolerably large edge chips occur. In the burnt state, there is the possibility of cutting, which is too expensive due to the great volume removed by cutting. Another possibility is the manufacture of the top and bottom rabbets by a plurality of cuts using a circular saw. The panel is cut to length in the first cut at each panel end; these cuts are not complicated and can be carried out at high precision simultaneously at the opposite panel ends, with as a rule the facade panels being pushed through under the two laterally arranged circular saws in a lying, transverse manner. Then, in a further workstep, one cut each is made from both sides at a right angle to the first cutxe2x80x94i.e. in the direction of the aperture. These cuts are carried out in the lying panel by two saw blades arranged at both sides with a cut depth which corresponds to the height of the top or bottom rabbet. These cuts can also be made simultaneously at high precision. The respective third cut at each end of the facade panel must, however, be made from different directions, at the top end from the front side of the panel and at the bottom end from the rear side of the panel. A pair of forces results from the opposing actions of the saws which exerts a torque on the lying panels so that it is very difficult to fix the panels on the conveying device with the required precision. The consequence of this is a high reject rate by the exceeding of the permitted narrow dimensional tolerances. Ultimately, this can only be prevented by an extremely precise and stable fixing of the panels to the machine or by two additional, individual worksteps (cuts) under otherwise identical conditions. The manufacturing costs of top and bottom rabbets transversely to the direction of extrusion moulding by respectively three cuts at the burnt panels are additionally substantially increased by these complications of the asymmetrical exertion of force so that the upright version of the extrusion moulded faces with a vertical aperture arrangement thereby becomes considerably less economical than the oblong version with horizontal apertures and the top and bottom rabbets moulded on in the same workstep.
It is therefore the object of the invention to describe an extrusion moulded facade panel and a method for its manufacture whose rabbets are arranged transversely to their apertures, which meets the architectonic technical and physical construction requirements, but which can be manufactured at lower cost and with more precise dimensions.
This object is solved in accordance with this invention by the characteristics of the height (17) of the top rabbet (16) formed by the rear panel framework (13) being smaller than or equal to the height of the joint (19) visible from the facade front side (18). The advantage of this embodiment consists of the height of the top rabbet formed by the rear panel formwork being lower than the height of the joint visible from the front of the facade. A top rabbet of such a low height can be carried out by the use of a double saw blade. The outerxe2x80x94seen from the facade panelxe2x80x94saw blade has an engagement depth which is greater than the panel thickness; the inner saw blade extends only approximately to half the panel thickness, i.e., up to the inner surface of the rear panel formwork. In this way, a top rabbet remains with a height which corresponds to the thickness of the inner saw blade. The bottom end of the facade panel is simultaneously cut to shape by a further saw blade whose engagement depth is greater than the panel thickness. Due to the simultaneous engagement of both saws, a practical balance of the cutting forces acting on the facade panels results so that a precise cut is achieved at both ends. The balance of the cutting forces can also be increased by the use of a reinforced saw blade at the bottom of the panel. The state in the manufacturing process is shown in FIG. 1, with the upper side of the lying panel being arranged at the front side of the facade in the mounted state of FIG. 2.
In another preferred embodiment in accordance with FIG. 3, the facade panel has a bottom rabbet of lower height which is formed by the front panel formwork. The advantage of this embodiment is in the fact that the facade can be mounted with a particularly low horizontal joint visible from the front side.
In another embodiment of the invention in accordance with FIG. 4, the facade panels are formed with top and bottom rabbets (30, 31) at the front panel formwork (32, 33). This has the advantage that the bottom rabbet is formed as a drop rabbet and thereby the directing of the water to the rear of the facade is avoided by adhesion to the lower edge. At the same time, the formation of very narrow joints at the front side is possible if this is wanted for architectonic reasons.
In another aspect of the invention in accordance with FIG. 5, the top and bottom rabbets are formed by the rear panel formwork. This has the advantage that wide horizontal joints visible from the front side can be formed, but that the actual open joint gap can be kept narrow.
The aspect of the facade panel in accordance with the invention is particularly advantageous in that the height of the joint visible from the front side is relatively small in relation to the thickness of the front panel formwork; at least smaller than twice the thickness of the front panel formwork. In this way, the view into the elongate apertures of the facade panels is obstructed.
In addition, in a further advantageous aspect of the invention, the thickness of the front panel formwork is relatively small in relation to the depth of the elongate apertures; at least smaller than one and a half times the depth of the elongate apertures. In this way, inherent weight is saved.
In another advantageous embodiment of the facade panel in accordance with the invention, the top and bottom rabbets are formed by cuts inclined slightly obliquely towards the front side of the panel, with the height of the top or bottom rabbet formed by the oblique cut being smaller than the height of the horizontal joint visible from the front side of the facade. The advantage of this embodiment can be found in the fact that no double saw blade is needed.